Flying QuietFlying Quiet

Noise Abatement Basics

August 5, 2000By Christopher L. Parker

We all want to live in a safer, cleaner world with less pollution, including noise pollution. As a result, many municipalities across the country are enacting noise abatement programs at local airports large and small. The stated purpose of these programs is to reduce airport noise and improve airport compatibility with the surrounding communities. This is a serious goal. And make no mistake about it, these programs are strictly enforced. At one airport in the Los Angeles basin, for example, a pilot can be cited with a misdemeanor for performing a full-stop landing followed by a taxi back to a runway under certain circumstances. This raises the question: What do pilots really need to know about noise abatement?

The Laws

To enforce a noise abatement policy, a local ordinance must be added to the city's municipal code. This ordinance provides for due process to ensure equitable and reasonable enforcement, and it lays out the details for implementing the noise abatement effort. It may also set forth maximum noise levels and prohibit or restrict certain aircraft operations such as touch and goes, low approaches, etc.

Generally, pilots can be cited for exceeding noise limits and/or performing an operation when it is prohibited or restricted. First-time violations typically result in a warning letter being sent to the registered owner of the aircraft. This letter explains the airport's noise abatement policy and requests that the pilot call the noise abatement office. Further violations can result in fines and even misdemeanor charges. Excessive violations may result in the aircraft and/or pilot being banned from the airport. An appeal procedure is usually provided.

The federal 1990 Airport Noise and Capacity Act requires that local noise abatement ordinances be approved by the FAA before they are enacted. Communities that had airport noise abatement laws on the books before 1990 were not obliged to meet the new requirements. But communities that want to create noise abatement programs today must get approval from the FAA. In addition, Part 36 of the federal aviation regulations sets maximum "flyover" noise limits for small aircraft manufactured after 1980. Even if an aircraft meets these noise standards, it may not be acceptable for operations at a given airport. It must comply with the local laws, even if they are more stringent than FAA standards.

The only time a pilot is likely to deal directly with the FAA over noise abatement issues is when air traffic controllers, usually tower controllers, get involved. Controllers often work with cities to advise pilots that a certain operation would violate local law. At that point, it's up to pilots whether they want to perform the operation in question, since controllers will generally grant the clearance if it doesn't violate federal aviation regulations.

Spreading The Word

Since almost all noise violations are committed by transient aircraft, noise abatement officials must work diligently to get the word out to pilots about their programs. They accomplish this by publishing their noise abatement procedures in as many pilot guides as possible. For example, Long Beach, California, publishes its procedures in at least 10 such guides in the hope that pilots will be exposed to the noise abatement rules before visiting the airport.

The official guide to flight information is, of course, the Airport/Facility Directory (A/FD), which lists noise abatement policies and procedures under "airport remarks." Noise abatement information can also be found in both the printed and online versions of AOPA's Airport Directory (http://data. aopa2.org/airport/index.cfm) and on the back of Jeppesen instrument approach plates. In addition, ATIS (automatic terminal information service) broadcasts often include advisories that noise abatement procedures are in effect. Some airports are also placing their noise abatement information on the Internet.

Noise ordinances vary, so pilots who plan to fly into an airport with a noise abatement program should call the airport's noise abatement office ahead of time to find out the details of its particular policy. Once at the airport, a visit to the noise abatement office can be informative and interesting. Noise control specialists are more than happy to explain noise abatement programs.

Understanding Noise

Before a noise abatement program can be enacted and enforced, officials need to know how much noise is being generated. Noise monitoring systems typically consist of microphones strategically located in noise-sensitive neighborhoods around the airport. These microphones transmit sound to a multi-track tape recorder, which records aircraft noise and the conversations taking place on tower, ground, and approach control frequencies 24 hours a day.

This information gathered from the air traffic control frequencies is essential in positively identifying an excessively noisy aircraft. A computer system analyzes the noise levels from the microphones, keeps track of noise events, identifies noise violations, and stores noise data. Using a system like this, a noise control specialist can easily track down an offending aircraft, and eventually, its pilot.

Pilots who understand a little about how sound works can use the laws of physics to their advantage. The decibel (dB), named in honor of Alexander Graham Bell, the inventor of the telephone, is the basic unit for measuring the relative loudness of sound. Normal conversation is about 60 dB while a rock group is about 110 dB. Because noise is measured on a logarithmic rather than linear scale, a change in sound as small 3 dB is easily discerned. A 10 dB increase in sound level is a very large increase in "loudness," not a 10 percent increase. So the bottom line is that every dB counts.

Another term used to describe sound is the single event noise exposure level (SENEL). This figure, reported in dB, measures not only how noisy an aircraft is, but also how long the noise event lasts. An event is the time from which a sound is first heard above the background noise until it disappears. Some ordinances limit maximum noise levels, others limit SENEL, and some limit both.

SENEL could be described as an annoyance index. Consider an example: A sonic boom is very loud, perhaps 100 dB or more, but it only lasts a second or two. Startling, but not that annoying. A leaf blower outside your bedroom window at 6:30 a.m., on the other hand, is annoying. The leaf blower is not as loud as the sonic boom, but its noise lasts longer.

All sound travels through a medium such as air or water. In air, the sound level decreases about 6 dB if the distance between the source (an airplane) and the receiver (a homeowner) is doubled. But sound travels more readily through warm and/or moist air (up to 5 dB of variation), so aircraft departures under instrument meteorological conditions or on humid summer afternoons may be louder than other departures.

Reducing The Noise

A key tactic in noise abatement is to put as much distance as possible between your aircraft and noise monitors. On takeoff, gaining altitude quickly while still within the airport's boundaries is paramount. Request the longest runway available and line up using every foot of it. Do not accept intersection departures. In most cases, best performance is obtained by applying maximum takeoff power prior to brake release. Keep in mind that high density altitude, calm winds, and heavy weight adversely affect climb performance, decreasing your aircraft's altitude over the monitors.

Use the takeoff technique recommended by the pilot's operating handbook. Climb out at your best angle or rate-of-climb speed, depending on the results of a noise test. Most noise abatement programs allow for testing during which you cannot be cited for violating the noise ordinance. A noise test allows you to determine which configuration, airspeed, power setting, and flight path will enable you to fly safely and comply with the noise limits. Before you conduct a test, get approval from the airport's noise abatement office.

During touch and goes, plan your touchdown for the first third of the runway. Landing long means you have less time to gain altitude before you pass over the monitors after you "go." After takeoff, avoid overflying the monitors by making appropriate departure turns. Noise abatement offices usually have maps that show the location of monitors and noise-sensitive areas. Smart pilots know where the monitors are located.

Pilots who fly or plan to get checked out in high-performance aircraft should be especially cautious. After reaching a safe altitude, preferably while within the airport's boundaries, accelerate to cruise-climb airspeed and set cruise-climb power. This will reduce the duration of the overflight and its SENEL.

While en route, stay at least 2,000 feet above ground level over noise-sensitive areas. When landing, use what are sometimes called "low-energy, high profile" descents. In other words, reduce power and make a steep descent. Again, consult the pilot's operating handbook for the correct technique. Delay using flaps until necessary so that you don't end up using excessive power to maintain speed and altitude. Finally, remember that you, the pilot, are the final authority for the safe operation of the aircraft. Don't compromise safety for noise abatement.

The future of many general aviation airports depends heavily upon the public's perception of them. Noise abatement programs help alleviate the public's concern over aircraft noise while balancing the needs of airport users and the interests of local residents. By using the noise abatement techniques presented here, we, as pilots, can make a positive contribution to the quality of our environment and the survival of general aviation.